This invention is directed to the field of developments known as elastomeric electrical connectors, where such connectors were introduced in the 1970's, as evidenced by U.S. Pat. No. 3,985,413, to Evans and owned by the assignee hereof. A commercial product, embodying the principles of Evans, is marketed under the name AMPLIFLEX, a trademark owned by The Whitaker Corporation, Wilmington, Del., and licensed to AMP Incorporated, Harrisburg, Pa.
Elastomeric connectors are made of conductive surface patterns supported by insulating silicone rubber. Electrical contact is made by positioning the elastomeric element between substrates and applying a low contact pressure to generate the required normal force. More precisely, the AMPLIFLEX connector utilizes a thin flexible polyamide film--on which are individual parallel lines of 1/2 or 1.0 oz. etched copper circuitry plated with gold over nickel--wrapped around a soft, non-conducting silicone core. The core is formulated to resist permanent set under long term compression.
As illustrated in the patent to Evans, the film is wrapped around the elastomeric core where the end portions are joined together. The end portions of the film are against each other and extend radially with respect to the body to form a tab. The opposed surfaces of these end portions are bonded to each other by a bonding material which is fused to the surfaces and the end portions. It will be appreciated that the conductors are of a uniform length and have their ends in alignment. These ends do not extend to the side edges of the film so that there is a bend of film adjacent to the free end of the tab which is devoid of conductors.
One of the shortcomings of the elastomeric connectors available commercially is that they exhibit a limited compression range. Typically such connectors are placed between a pair of parallel walls where the free or open ends are compressed between a pair of planar electronic devices, such as printed circuit boards. It will be understood that the elastomeric connector is thusly squeezed from four sides into the confined space between said parallel walls. By the use of a solid core, as taught by Evans, the core must be deflected since the silicone elastomeric material is hydraulic in nature. This results in a very high force at very early stages of deflection of the planar electronic devices. If the cavity or space containing the connector is filled, a significant amount of force results for a small additional deflection. This additional force can impact on the planar electronic devices causing them to bow or warp.
The present invention, by the inclusion of a space or hole about or within the core, allows the core to be deflected inward, into the space or hole, giving it a greater range of deflection retiring a lower necessary force.
The advantages of this invention will become apparent from the specification which follows, particularly when read in conjunction with the accompanying drawings.